Under the first location it stores the region (1 - Region A, 2 - Region B, 4 - Region C).The number of remaining changes is stored under the second location. Every time you change region in PowerDVD, this number is decremented by 1. You can just put there something like FFFF (65535 changes) or better 1869F (99999 changes) and forget about it.

By default, there are no values in both locations. PowerDVD interprets this as Region A and 5 remaining changes. When you change region for the first time, it puts values there.

In Vista, region information is stored in Alternate Data Stream (ADS) attached to the file "CLDShowX.ini" located in "C:\ProgramData\CyberLink\PowerDVD\". You can view the content of that stream using, for example, "ADSLocator.exe" utility. If you run out of the number of remaining changes, just delete that file. Next time you start PowerDVD, it will be recreated with default setting.

II. WinDVD BD for VAIO Ver.8.0.08.100

1) Download a program called "Autoruns" from www.sysinternals.com .
2) Run Autoruns.exe, go to "Drivers" tab and disable driver called "regi"
(regi.sys). Just untick the checkbox next to it.
Note: DO NOT delete it.
3) Restart Windows.
4) Delete file "ivireg.ivr" in "C:\Windows\System32\" folder.
5) Re-enable "regi" driver using Autoruns (tick the checkbox).
6) Restart Windows.File "ivireg.ivr" will be recreated with default settings and
you can change BD region from WinDVD interface 5 more times before you
have to repeat this procedure. Enjoy!
P.S.: If you have a dual boot system (say, XP and Vista), you can just boot to another OS and delete "ivireg.ivr" from there.